Manufacture of flat glass



Dec. 14, 1965 R. BARRADELL-sMlTl-i ETAL 3,223,503

MNUFACTURE OF FLAT GLASS Filed Aug. lO, 1960 Z5 Sheets-Sheet 1 Dec. 14, 1965 R. BARRADELL-SMITH ETAL 3,223,503

MNUFACTURE OF FLAT GLASS Filed Aug. lO, 1960 5 Sheets-Sheet 2 Fig/ .39 A

A torneys Dec 14, 1965 R. BARRADELL-SMITH ETAL 3,223,503

MANUFACTURE OF FLAT GLASS Filed Aug. lO, 1960 3 Sheets-Sheet I5 Mam www,

n s By W A llorneys United States Patent O 3,223,503 MANUFACTURE F FLAT GLASS Richard Barradell-Smith, St. Helens, and Frederick William Silverwood, Appley Bridge, England, assignors to Pilkington Brothers Limited, Liverpool, England, a British company Filed Aug. 10, 1960, Ser. No. 48,662 Claims priority, application Great Britain, Aug. 28, 1959, 29,514/ 59 9 Claims. (Cl. 65-99) This invention relates to the manufacture from glass forming substances of flat material in ribbon form.

In the manufacture of fiat glass in ribbon form during which the ribbon is in contact with a molten bath chemically inert to the ribbon, the width of the bath surface being greater than the width of the ribbon, there is a length of the ribbon of glass whose viscosity is such that the ribbon is susceptible of deformation on the bath surface by the formation of long radius bends, or to drift from a desired path down the bath due to the inability of the ribbon to resist lateral forces which are generally speaking due to convection currents in the molten bath or to hydrodynamic instability.

A main object of the present invention is to assist in maintaining the ribbon in a desired path as it is advanced along the bath, and create conditions whereby a dirigible ribbon persists on the bath.

In the manufacture, according to the present invention, from glass forming substances of flat material in ribbon form vduring which the material in ribbon form is in contact with a molten bath chemically inert to the ribbon, the width of the bath surface being greater than the width of the ribbon, steering forces are developed which operate at the surface of the bath at least in localities where the ribbon is deformable, which forces act on the ribbon in a direction across its intended path as it is advanced along the bath.

The present invention is particularly suitable for the manufacture of flat glass in ribbon form having a lustre of fire nish quality during which the ribbon is in Contact with a bath of molten metal, but in referring to glass forming substances in this description and in the statements of invention the expression is intended to include substances which form inorganic materials comprising vitreous and crystalling particles in Whatever proportions.

In the application of the present invention to the manufacture of at glass having a lustre of re finish quality during which the glass is in contact with a bath of molten metal contained in a tank structure over which bath a protecting atmosphere is maintained, the Width of the bath surface being greater than the width of the ribbon, steering forces are developed which operate at the surface of the bath at least in localities where the ribbon is deformable, which forces act on the ribbon in a direction across its intended path as it is advanced along the bath.

The steering forces may be developed by selectively modifying the temperature of the bath in localities where the ribbon is susceptible of deformation, The modification of the temperature of the bath may be effected by a heater or cooler located singly or in pairs underneath the ribbon of glass so as to develop steering forces which operate at the surface of the bath. Preferably the ternperature of the bath is modied in the vicinity of at least one edge of the deformable part of the ribbon.

The present invention also comprehends the step of selectively modifying the temperature of the molten bath lCe at the surface in the vicinity of at least one edge of the ribbon, so that the intensity of the convection currents, engendered in the bath and moving in a direction across the intended path of the ribbon at the surface of the bath, is modied to develop steering forces which operate at the surface of the bath where the ribbon is dirigible and which forces act on the ribbon in a direction across its intended path as it is advanced along the bath.

The temperature of the bath may be modied by varying the depth of heat exchange effected in the vicinity of at least one edge of the ribbon. Alternatively the temperature may be modified according to the invention by varying the distance from the edge or edges of the ribbon at which the heat exchange is achieved, or by confining a flowing medium in heat exchange relationship With the bath in the vicinity of at least one edge of the ribbon and modifying the extent of the heat exchange yand varying the rate of flow of the medium and/or the temperature of the medium.

The invention further comprehends a sheet of fiat glass produced from a ribbon manufactured in the above stated manner.

In order that the invention may be more clearly understood one preferred embodiment will now be described by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a central longitudinal sectional elevation of apparatus for use in the manufacture of flat glass in ribbon form on a bath of molten metal contained in a tank structure, such apparatus including a roof structure superimposed on .the tank structure which roof maintains a protecting atmosphere over the bath,

FIGURE 2 is a plan View of the tank structure shown in FIGURE l in which plan view is more clearly indicated the positions of control elements,

FIGURE 3 is a detail sectional side elevation, to a much larger scale than that of FIGURES 1 and 2, for the sake of clarity, taken on the line III to III of FIG- URE 4, showing the supports for vertically and horizontally adjusting the control elements,

FIGURE 4 is a front elevation taken on the line IV-IV of FIGURE 5,

FIGURE 5 is a plan of the constructional arrangement shown in FIGURES 3 and 4, and

FIGURE 6 is a perspective View to a smaller scale more clearly showing the form of the control element illustrated in FIGURE 3.

In the drawings like references designate the same 0r similar parts.

In the apparatus illustrated in FIGURES l and 2 conventional means are shown for forming a ribbon of glass 1, the conventional means comprising a fore-hearth 2 and casting rolls 3, 4. The glass in ribbon form leaving the casting rolls is advanced by them on to a bath 5 of molten metal contained in a tank structure, which bath is at an elevated temperature and of a specific gravity such that the ribbon of glass leaving the casting rolls forms a layer 1a of glass which fioats on the bath.

The tank structure comprises a floor 6, end walls'7, 8 and side Walls 9 which walls contain the bath of molten metal, and over the tank structure is a roof structure of sectional form, the sections being indicated at 10, the roof structure defining a headspace over the bath in which a protecting gas is maintained.

At the ends of the roof structure and between the roof sections, tweels are provided, indicated at 11 12, 13, 14 and 15 which sectionalise the headspace in order to `facilitate temperature regulation along the bath. The protecting gas is admitted through pipes comprising ducting 16 connecting branches 17 and headers 18, which are connected to a suitable source of supply, not shown. The protecting gas admitted into the headspace is a gas which will not chemically react with the substance from which the bath is formed to produce contaminants of the glass, for example metal oxides or sulphides. The gas can be supplied through the ducting to afford a non-oxidising atmosphere over the bath when the bath is formed of a readily oxidisable metal, such as tin or alloys of tin on which the ribbon of glass can float, and by providing a plenum in the headspace within the roof structure, ingress to the headspace within the roof structure, ingress to the headspace of atmospheric air is prevented.

When the glass 1 is advanced from the casting rolls 3, 4 it -forms a plastic layer 1a which layer as it is advanced becomes more and more fluid and in a molten state spreads unhindered on the bath, due to the elevated temperature of the bath which is a temperature of about l000 C. to 1,100" C., between the tweels 11 and 12, and as the width of the bath is greater than the maximum width of the ribbon there is developed a buoyant body 1b of fully fluid molten glass of stable thickness which, because of the regulated feed is continually advanced along the bath in ribbon form. At the tweel 12,

l the temperature is about 1,000 C. and the fully fluid molten glass in ribbon form 1c which emanates from the fluid buoyant body 1b of stable thickness is progressively advanced along the substantially frictionless surface of the bath.

In that part of the bath between the tweels 12 and 13 the glass has cooled to about 825 C. at which point the ribbon part 1d is becoming rm but is still in a plastic state and could be deformed from the desired str-aight edge for, but between the tweels 13 and 14 the glass has progressively cooled to about 650 C. where the ribbon part 1e is fairly stiff (the viscosity being about 107 poises) and passes under the tweel 14 on its way to the exit from the bath, and thence to a lehr to which it is carried from the bath by traction rolls 19, 20 Without damage to the glass.

In FIGURE 2 is clearly illustrated at the parts indicated by the reference 21 where the side edges of the molten layer 1a naturally spread on the bath due to the high temperature of the bath, to `form the buoyant body V1b of stable thickness, the area of which is roughly which protrude through the furnace structure and an intermediate part connecting the two arms. In the example described the intermediate .part is straight, but the intermediate part may have a dilerent shape, for example it may be in the form of a helix.

In FIGURES 1 and 2 location of these coolers is indicated diagrammatically by lines 23 (parallel to the side walls 9) with which are conjoined parallel lines 24 passing through the tank structure, these lines representing respectively the intermediate parts of the control elements and the arms for manipulating the intermediate parts, hereinafter described with particular referenceY to FIGURES 3 to 6. As clearly shown in FIGURE 2 the control elements are disposed alongside the deformable part 1b, 1c, 1d of the ribbon which is developed from the layer 1a and ends about the tweel 13, and accordingly in a state to be susceptible to the effects of variable lsteering forces for the nature herein described.

In the construction illustrated in FIGURES 3-6 the .control element is formed by bending a tube on itself to form the two arms 24 and the straight intermediate part 23 comprised in an offset portion of the arms where it is bent upon itself. The straight part 23 is located at or near the surface of the bath 5 and is movable with respect to the edge of the ribbon by axial displacement to or from the ribbon, as indicated by the arrow 25 in FIGURE 3.

As indicated in FIGURE 3 the ends of the arms 24 are each connected by hose 26 held on to the arms 24 by clips 27 to a cold water supply so that the water can enter one of the arms, liow through the control element, in particular through the straight part 23, and back out through the other arm, whereby the straight part 23 is maintained in relatively cold condition.

The control elements comprising the parts 23, 24, 24 are mounted to be vertically adjustable so that the part 23 can be more or less immersed at the surface of the molten bath and thereby vary the superficial area of the part 23 in heat exchange relation with the bath and thus modify the effect on the intensity of the convection current to develop steering forces which operate at the surface of the bath, that is at theexposed surface of the molten metal at the sides of the ribbon of glass and/or at the surface of the molten metal and the metal/glass interface. Accordingly the tank structure comprises a vertical elongated aperture 28 of a size to permit the desired lateral displacement in a vertical plane, and in order to prevent contamination of the gases over the bath or loss of the gases from the bath through the passage 28, a plate 29 is mounted on the structure and over the passage and carries a cylindrical socket 30 which is offset upwardly with respect to the plate 29, and carries one end of a flexible container 31, preferably of concertina form, as shown, the other end of which is connected to the respective arm 24.

Clamping bands 32 and 33 respectively hold the extremities of the flexible containers to the socket and to the arm so that a gas-tight joint is formed about the socket and the arm, which joint functions throughout the permitted adjustments of the arms in a vertical plane, or the permitted adjustments of the arms in a horizontal plane, that is in an axial direction.

From the foregoing it will be appreciated that the socket 30 has a diameter suiciently great to permit the desired angular adjustment of the arms in a vertical plane, i.e. with respect to the passage 28. As clearly shown in FIGURE 3 the arms are so disposed that the straight part 23 intersects the surface of the bath and can be displaced with respect to the surface and/0r with respect to the adjacent edge of the ribbon, as clearly shown in chain lines 34 and 35.

Experiments have shown that when cold water is generously supplied through the arms, the straight part 23 should be localised not more than 6" from the respective edge of the ribbon to impose a drag which steers the ribbon of glass in a desired path on the bath. It may be nearer to the edge and instead of resting on the surface of the bath, may be partially or wholly immersed at the surface and the reference herein to selectively cooling the bath in the vicinity of the edges the ribbon, includes the disposal of the control elements so that the straight parts 23 are not more than 6 from the ribbon edge when the straight part is about one foot in length. However it will be appreciated that should the control of the ribbon by the transverse steering forces not be quick enough to eliminate drift the straight parts 23 will act as nonwettable fenders, and can be moved laterally of the bath to apply lateral forces to the ribbon to steer it back into its desired path on the bath.

The vertically adjustable support for the arms is mounted on a stub 36, adjustably carried in a socket 37 carried by the tank structure, the stub carrying a threaded stud 38 on which a clamping nut 39 is mounted. The vertical adjustment comprises in the upper part a slotted stem 40 which is passed over the stud 38 and clamped against the stub 36 by the clamping means 39. The slotted stem 40 5. emanates from a bridge 41 carrying two depending plates 42 which are slotted at their lower ends, as indicated at 43, for the passage of the arms 24. The slotted stem 40 and the clamping nut 39 provide means for rapidly lifting the control element in case of emergency.

In the bottom part of the plates 42 is a set-screw 44 which is used to set the arms in desired relationship with the plates. By such arrangement the first setting of the arms can be eifected by utilising the clamping member 30 and finer adjustment effected by using the set-screws 44. Thereby the degree of immersion of the straight intermediate parts 23 of the control elements in the bath can be precisely prescribed, and if necessary precise alignment of the straight part 23 with the surface of the bath effected by operating the set screws 44.

For setting the arms in an axial adjustment with respect to the edge of the deformable part of the ribbon 1b, 1c or 1d collars 45 are provided on the arms so that they can be secured in desired relationship with the vertical support. The arms 21 are preferably braced together, as most clearly indicated in FIGURE 4, the bracing consisting of two offset bars 46 and 47 which are centrally clamped together by actuating a threaded rod 48. This bracing apart from assuring parallelism of the arms during tilting affords a counterweight which maintains the arms against the fulcrum constituted by the inner edge of the plates 29.

Conveniently, as clearly shown in FIGURES 3 and 6, the outer end of the arms 24 are downwardly bent in vertical planes to constitute handles 49 which facilitate axial displacement of the arms to determine the setting of the spaced relation of the respective straight part 23 in relation to the adjacent edge of the glass ribbon.

Experiments have shown that any drag applied to the deformable part of the ribbon, i.'e. parts 1b, 1c or 1d by the transverse steering forces developed at the surface of the molten metal can be modified by adjusting the parts 23 of the control elements with respect to either or both edges of the ribbon of glass, and thereby assist in maintaining in a desired path as it is advanced along the bath or guiding it in the desired path. Thus a completely dirigible ribbon is maintained on the bath.

Although in FIGURE 2 the control elements are shown disposed in pairs, one element on each side of the ribbon, the elements may be disposed in staggered relation along the ribbon, so long as the application of the control elements near one edge develops steering forces which operate at the surface from the centre of the bath towards the respective wall of the tank structure by intensifying the convection current, to give the desired urge to the ribbon towards that wall. This control from one side may be accompanied by retracting the control element on the other side of the ribbon to minimise the convection ow towards that wall of the tank structure, the arrangement of the intermediate part of the control elements need not be symmetrical with respect to the ribbon, nor need they be all of the same length, for example, according to thermal conditions outside the tank, on one side of the ribbon two control elements may be employed in spaced relation of which the total length of the straight parts 25 is about the same as that part on one control element on the opposite side of the ribbon.

In accordance with the invention many elements in spaced relation at each side of the dirigible ribbon are employed to achieve maximum flexibility of control along those parts of the ribbon where the ribbon of glass is susceptible of deformation as already explained, and could be deformed unless the controls were applied to indirectly guide the ribbon.

The control elements employed according to the present invention are preferably formed from stainless steel tubing, but high silica glass tubing may be employed.

Further, although in the embodiment described herein reference has been made to the connection of the control elements to a cold water supply, it will be understood that if the local temperature in the bath is to be raised, a gaseous heating medium may be supplied to the control element.

In FIGURE l, at 50 and 51, are respectively indicated thermal devices for obtaining the required temperature gradient in the bath and the corresponding temperatures in the head space over the bath.

We claim:

1. In the manufacture from glass forming substances of fiat material in ribbon form duringwhich the material in molten ribbon form is in contact with a bath of molten metal, while the ribbon is being advanced lengthwise along said bath, the width of the bath surface being greater than the width of the ribbon at least in localities where the ribbon is deformable, and the length of the deformable ribbon in said bath of molten metal being suiciently great to tend to cause said ribbon in said localities to drift edgewise of its intended path, the step of creating surface movement of the molten metal of the bath across the intended path of the ribbon at least in -said localities where there i-s said drifting tendency, so that transverse surface movement of the molten metal in contact with the underface of the ribbon acts to maintain the ribbon in its intended path as it is advanced along the bath.

2. In the manufacture from glass forming substances of flat material in ribbon form having a lustre of lireiinish quality, during which manufacture the material in molten form is floated on a bath of molten metal over which 'bath a protecting atmosphere is maintained, While the ribbon is being advanced lengthwise along said bath, the width of the bath surface being greater than the width of the ribbon at least in localities where the ribbon is deformable, and the length of the deformable ribbon in said bath of the molten metal being suiciently great to tend to cause said ribbon in said localities to drift edgewise of its intended path, the step of creating surface movement of the molten metal :of the bath across the intended path of the ribbon, at least in said localities where there is said drifting tendency, so that transverse surface movement of the molten metal in contact with the underface of the ribbon applies steering forces to the ribbon, which forces `act to maintain the ribbon in its intended path as it is advanced along the bath.

3. In the manufacture of at glass in ribbon form having a lustre of fire-finish quality, during which manufacture, glass in molten form is oated on a bath of molten metal over which bath a protecting atmosphere is maintained, and is advanced in ribbon form lengthwise along said bath, the width of the bath surface being greater than the width of the ribbon at least in localities where the ribbon is deformable, and the length of the deformable ribbon in said bath of molten metal being suiiciently great to tend to cause said ribbon in said localities to drift edgewise of its intended path, the step -of selectively effecting heat exchange with the bath in said localities where there is said drifting tendency, at least yat one side of the ribbon of glass and in different zones spaced apart along the path of the ribbon, thereby to modify selectively the intensity of transverse convection currents at the surface of the molten metal, which currents apply steering forces to the ribbon in a direction across its intended path as it is advanced along the bath.

4. A method according to claim 3, characterized by selectively modifying the temperature of the bath in the vicinity of at least one edge of the ribbon. p

5. A method according to claim 3, characterized by selectively modifying the temperature of the bath at the surface of the bath in the vicinity of at least one edge of the ribbon.

6. A method according to claim 3, characterized by selectively modifying the temperature of the bath by varying the depth of heat exchange effected in the vicinity of at least one edge of the ribbon.

7. A method according to claim 3, characterized by varying the distance from the edge or edges of the ribbon at which the heat exchange is achieved.

8. A method according to claim 4, characterized by selectively modifying the temperature of the bath by conning a owing medium in heat exchange relationship with the bath in the vicinity of at least -one edge of the ribbon and modifying the extent of the heat exchange by varying the rate of flow of the medium.

9. A method according to claim 4, characterized by selectively modifying the temperature of the bath by confining a owing medium in heat exchange relationship with the bath in the vicinity of at least -one edge of the ribbon and modifying the extent of the heat exchange by varying the temperature of the medium.

8 References Cited by the Examiner UNITED STATES PATENTS 710,357 9/1902 Heal. 1,564,240 12/1925A Hitchcock 65-182 1,790,774 2/1931 Spinasse 65-201 X 2,164,048 6/1939 Bertrand 65-20l FOREIGN PATENTS 567,339 11/1958 Great Britain,

DONALL H. SYLVESTER, Primary Examiner.

ARTHUR P. KENT, Examiner.

DANIEL M. PRITCHE'I'T, DANIEL CRUPAIN,

Assistant Examiners. 

1. IN THE MANUFACTURE FROM GLASS FORMING SUBSTANCES OF FLAT MATERIAL IN RIBBON FORM DURING WHICH THE MATERIAL IN MOLTEN RIBBON FORM IS IN CONTACT WITH A BATH OF MOLTEN METAL, WHILE THE RIBBON IS BEING ADVANCED LENGTHWISE ALONG SAID BATH, THE WIDTH OF THE BATH SURFACE BEING GREATER THAN THE WIDTH OF THE RIBBON AT LEAST IN LOCALITIES WHERE THE RIBBON IS DEFORMABLE, AND THE LENGTH OF THE DEFORMABLE RIBBON IN SAID BATH OF MOLTEN METAL BEING SUFFICIENTLY GREAT TO TEND TO CAUSE SAID RIBBON IN SAID LOCALITIES TO DRIFT EDGEWISE OF ITS INTENDED PATH, THE STEP OF CREATING SURFACE MOVEMENT OF THE MOLTEN METAL OF HTE BATH ACROSS THE INTENDED PATH OF THE RIBBON AT LEAST IN SAID LOCALITIES WHERE THERE IS SAID DRIFTING TENDENCY, SO THAT TRANSVERSE SURFACE MOVEMENT OF HTE MOLTEN METAL IN CONTACT WITH THE UNDERFACE OF THE RIBBON ACTS TO MAINTAIN THE RIBBON IN ITS INTENDED PATHS AS IT IS ADVANCED ALONG THE BATH. 